Typing of blood is one of the most frequent and important laboratory techniques of medicine. Typing is based on a specific hemagglutination assay using erythrocytes from patients to be typed with human polyclonal antisera, i.e., anti-A and anti-B sera. Due to the variability and limited availability of human reagents, it has been of interest to develop standardized reagents which can be supplied in unlimited quantities. Recent developments in hybridoma antibody technology have enabled the development of various monoclonal antibodies with anti-A properties. However, these monoclonal anti-A antibodies generally fail to agglutinate the minor blood group A subgroups.
Blood group A has been subgrouped into the major subgroups A.sub.1 and A.sub.2 and minor subgroups A.sub.3-5 and A.sub.x (see Race, R. R. et al, Blood Groups in Man, 6th Ed., pp. 9-13, Blackwell Scientific Publications, Oxford (1975)). The chemical difference between the two major phenotypes A.sub.1 and A.sub.2 has not been clarified, although several studies have indicated both quantitative (see Makela, O. et al, J. Immunol., 102:763-771 (1969) and Economidou, J. et al, Vox Sang., 12:321-328 (1967) and qualitative (see Economidou, J. et al, Vox Sang., 12:321-328 (1967): Mohn, J. F. et al, Human Blood Groups, pp. 316-325, Eds. Mohn, J. et al, Karger, Basel (1977); Moreno, C. et al, J. Exp. Med., 134:439-457 (1971) and Kisailus, E. C. et al, J. Exp. Med., 147:830-843 (1978) differences in the expression of A antigen.
A large number of laboratories in the United States and other countries have attempted to develop monoclonal antibodies to cover minor A.sub.3 -A.sub.5 and A.sub.x subgroups but to date, no satisfactory reagent has been produced.